Flanked by four children from across the country, President Obama today unveiled a sweeping plan to curb gun violence in America through an extensive package of legislation and executive actions not seen since the 1960s.

Obama is asking Congress to implement mandatory background checks for all gun purchases, including private sales; reinstate a ban on some assault-style weapons; ban high-capacity magazines holding more than 10 rounds; and crackdown on illicit weapons trafficking.

The president's proposal also includes new initiatives for school safety, including a call for more federal aid to states for hiring so-called school resource officers (police), counselors and psychologists, and improved access to mental health care.

Obama also initiated 23 executive actions on gun violence, policy directives not needing congressional approval. Among them is a directive to federal agencies to beef up the national criminal background-check system and a memorandum lifting a freeze on gun violence research at the Centers for Disease Control and Prevention.

"I intend to use whatever weight this office holds to make them a reality," Obama said at a midday event in a White House auditorium. "If there's even one thing that we can do to reduce this violence, if there's even one life that can be saved, then we have an obligation to try.

"And I'm going to do my part."

The announcement comes one month after a mass shooting at Sandy Hook Elementary School in Newtown, Conn., left 26 dead, including 20 children. Obama called it the worst moment of his presidency and promised "meaningful action" in response.

The proposals were the work of an Obama-appointed task force, led by Vice President Joe Biden, that held 22 meetings on gun violence in the past three weeks. The group received input from more than 220 organizations and dozens of elected officials, a senior administration official said.

As part of the push, Obama nominated a new director for the Bureau of Alcohol, Tobacco and Firearms, which leads enforcement of federal gun laws and has been without a confirmed director for six years. The president appointed acting director Todd Jones, the U.S. attorney for Minnesota, to the post, if the Senate confirms him.

The administration's plan calls for aid to states for the hiring of more school resource officers, counselors and psychologists. Obama also directed the Department of Education to ensure all schools have improved emergency-response plans.

He also called on Congress to make it illegal to possess or transfer armor-piercing bullets; it's now only illegal to produce them.

Officials said some of the legislative measures Obama outlined could be introduced on Capitol Hill next week. The price tag for Obama's entire package is $500 million, the White House said.

"House committees of jurisdiction will review these recommendations," a spokesman for House Speaker John Boehner said in response to Obama's announcement. "And if the Senate passes a bill, we will also take a look at that."

The proposals are already being met with stiff opposition from gun rights advocates, led by the National Rifle Association, which overnight released a scathing ad attacking the president as an "elitist hypocrite."

"Are the president's kids more important than yours?" the narrator of the NRA ad says. "Then why is he skeptical about putting armed security in our schools, when his kids are protected by armed guards at their school?"

Obama has questioned the value of placing more armed guards at schools around the country, although his proposal does call for placement of more police officers at public schools. The NRA opposes most of the other gun restrictions Obama has proposed.

"Keeping our children and society safe remains our top priority," the NRA said in a statement after Obama's announcement.

"Attacking firearms and ignoring children is not a solution to the crisis we face as a nation," the group said. "Only honest, law-abiding gun owners will be affected and our children will remain vulnerable to the inevitability of more tragedy."

Hurdles for Gun Laws in Congress

Many members of Congress from both parties are also skeptical that some of the proposed new restrictions on gun sales can be effective, much less pass.

"Nothing the president is proposing would have stopped the massacre at Sandy Hook," Republican Sen. Marco Rubio of Florida said. "President Obama is targeting the 2nd Amendment rights of law-abiding citizens instead of seriously addressing the real underlying causes of such violence."

Senate Majority Leader Harry Reid, a Democrat and gun owner, told a Las Vegas TV station Friday, "Is [the assault weapons ban] something that can pass the Senate? Maybe. Is it something that can pass the House? I doubt it. So I think there are things that we know we can do."

Before the announcement, the White House downplayed challenges facing individual aspects of gun-control proposals -- most notably the assault weapons ban -- stressing that no single measure can solve the epidemic of gun violence sweeping the country. They also pointed to successful steps on guns already taken on the state level.

New York State, for instance, approved the nation's most stringent gun-control law Tuesday, tightening a ban on assault-style weapons and beefing up protections to keep guns from the mentally ill.

Obama might travel the country seeking to leverage popular support for his proposals to urge action in Congress, officials said. He is also expected to mobilize his network of campaign supporters to participate in advocacy on guns.

"This will not happen unless the American people demand it," Obama said today of his plan. "If parents and teachers, police officers and pastors, if hunters and sportsmen, if responsible gun owners, if Americans of every background stand up and say, enough, we suffered too much pain and care too much about our children to allow this to continue, then change will come. That's what it's going to take."

Dozens of kids have written to the president about gun violence, officials said, including 8-year-old Grant Fritz of Maryland, who wrote in a letter released by the White House, "there should be some changes in the law with guns. It's a free country, but I recommend there needs be [sic] a limit with guns."

"Their voices should compel us to change," Obama said of the children.

Obama was joined for his announcement by seven cabinet secretaries, including Attorney General Eric Holder, Education Secretary Arne Duncan and Homeland Security Secretary Janet Napolitano, other local law enforcement leaders and mayors, and the families of victims and survivors of the Newtown shooting.

Popular Support for Gun Rules

Many of Obama's proposals have strong support in the latest ABC News-Washington Post poll released Monday.

New restrictions on high-capacity magazines are backed by 65 percent of Americans in the poll, with 58 percent supporting a ban on the sale of assault-style weapons. Thirty-nine percent oppose such a ban.

The NRA's proposal to place an armed guard in every school received 55 percent support in the survey.